1. Field of the Invention
The present invention generally relates to electromagnetic relays and, more particularly, to an electromagnetic relay suitable for an electric component incorporated into electric equipment for automobile.
Electromagnetic relays are incorporated into various equipments. Since a space into which an electromagnetic relay is accommodated has been reduced in connection with miniaturization of electric equipment, there is a demand for reducing heights of electromagnetic relays.
A maximum electric current of an electromagnetic relay used in electric equipment for automobile is required to be as high as 30 amperes. Such a high maximum electric current causes a large amount of heat generated in the electromagnetic relay, and it is necessary to achieve an efficient radiation of heat from the electromagnetic relay.
2. Description of the Related Art
FIG. 1 is a perspective view of a conventional electromagnetic relay 10 of electric equipment for automobile in a state where a cover is removed. FIG. 2 is a side view of the electromagnetic relay 10 shown in FIG. 1. In FIG. 1, directions X1 and X2 correspond to a direction of width of the electromagnetic relay 10; directions Y1 and Y2 correspond to a longitudinal direction; and directions Z1 and Z2 correspond to a direction of height.
The electromagnetic relay 10 comprises, as shown in FIG. 3, a subassembly 11, a base unit 30 and a terminal member 40 having a make fixed contact. The subassembly 11 is attached on the base unit 30, and the terminal member 40 is inserted from the X2 side.
The subassembly 11 comprises, as shown in FIG. 4, a plastic bobbin 12 on which a coil 13 is wound. An iron core 14, a yoke 16, a movable leaf spring/armature assembly 17 are incorporated into the bobbin 12. The coil 13, the iron core 14 and the yoke 16 together constitute an electromagnet.
The bobbin 12 has a square frame part 12a on the Y2 side and a square frame part 12b on the Y1 side. A hook part 12c is formed on a bottom part of the square frame part 12a. A cylindrical projection 12d is formed on a bottom part of the square frame part 12b. A coil terminals 25 and 26 are insert-molded with the square frame part 12b. 
The iron core 14 having an iron base plate 15 is incorporated into the bobbin 12 from the Y1 side. The L-shaped yoke 16 is incorporated into the bobbin 12 from the Y2 side, and an end of the iron core 14 is secured to the yoke by caulking. Additionally, the movable leaf spring/armature assembly 17 is attached to the bobbin 12 on the Y1 side.
The movable leaf spring/armature assembly 17 comprises a generally L-shaped movable leaf spring 20, a square armature 21 and a movable contact member 22. The movable leaf spring 20 comprises a main part 20a, a spring arm part 30b extending from the main part 20a in the Y2 direction and a common terminal 20c extending from the main part 20a in the Z2 direction. The armature 21 is fixed to a root of the spring arm part 20b. The movable contact member 22 is fixed on an end of the spring arm part 20b. The main part 20a is fixed to iron base plate 15 by caulking.
The base unit 30 has a structure in which a break fixed contact member 32 is insert-molded with a plastic base 31. A break terminal part 32a extends from the base 31 in the Z2 direction. A break fixed contact 33 is exposed on the break fixed contact member 32. The base 31 is provided with apertures 34 and 35 for attaching the subassembly 11. The base 31 is also provided with an aperture 36 and a notch 37 for attaching the terminal member 40 having the make fixed contact.
The terminal 40 wit the make fixed terminal has a generally L-shape, and comprises a make terminal part 40a, a concave part 40b and a make fixed contact member 41.
The subassembly 11 is attached to the base unit 30 by the cylindrical projection 12d being fit in the aperture 35 and the hook part 12c being fit in the aperture 34. The terminal 40 is attached to the attached to the base unit 30, after the subassembly 11 and base unit 30 are assembled together, by being inserted from the X2 side in a state in which the concave part 40b is fit in the aperture 36 and a root of the make terminal 40a is fit in the notch 37.
The yoke 16 is located under the coil 13, and the armature 21 is located under the yoke 16. Additionally, the movable contact member 22 contacts the break fixed contact member 32. The make fixed contact member 41 is located above the movable contact member 22. In the normal state, the common terminal part 20c and the break terminal part 32a are in a xe2x80x9cclosedxe2x80x9d state, and the common terminal part 20c and the make terminal part 40a are in an xe2x80x9copenxe2x80x9d state.
The electromagnetic relay 10 has a height h1 as shown in FIG. 1, and is mounted to a printed board in a state in which the terminals and terminal parts are inserted into through holes formed in the printed board.
When a current is supplied to the coil 13, the electromagnet is exited, and the armature 21 is magnetically attracted by the yoke 16. Accordingly, the spring arm part 20b is formed upward, which causes the movable contact member 22 being brought into contact with the make fixed contact member 41. Thereby, the state of the common terminal part 20c and the break terminal part 32a is changed to an xe2x80x9copenxe2x80x9d state, and the state of the common terminal part 20c and the make terminal part 40a is changed to a xe2x80x9cclosedxe2x80x9d state.
The conventional electromagnetic relay 10 shown in FIG. 1 has a problem in that it is difficult to reduce the height for the following reasons.
(1) The base unit 30 has a relatively large thickness t1 as shown in FIG. 1 so as to maintain a strength of engagement of the hook part 12c, which fixes the subassembly 11 to the base unit 30.
(2) The terminal member 40 is attached to the base 31 by the concave part 40b is fit in the aperture 36 and the root of the make terminal part 40a is fit in the notch 37. This structure for attaching the terminal member 40 cannot provide a high positioning accuracy of the terminal member 40. Additionally, since the member to which the terminal member 40 is attached is different from the member to which the yoke 16 is attached, a distance a between the make fixed contact member 41 and the yoke 16 tends to fluctuate when the electromagnetic relay 10 is assembled. Thus, the distance a between the make fixed contact member 41 and the yoke 16 is set larger than an actually necessary distance so as to maintain a sufficient withstand voltage, thereby increasing the height of the electromagnetic relay 10.
(3) Since the accuracy of attaching the terminal member 40 is not so high, a distance b between the make fixed contact member 41 and the break fixed contact member 32 is set larger than an actually required distance as shown in FIG. 2 so as to maintain a sufficient withstand voltage. This prevents a reduction in the height of the electromagnetic relay 10.
In the conventional electromagnetic relay 10 shown in FIG. 1, the coil 13 is excited so as to close the contact between the common terminal part 20c and the make terminal part 40a. When an electric current of 30 amperes flows through the contact, a large amount of heat is generated. The generated heat is transferred to and spread into the printed bard through the common terminal part 20c and the make terminal part 40a, and the heat is dispersed into the printed board, and is radiated to the atmosphere. However, a heat transmission path of the heat generated in the electromagnetic relay is small, and the resistance of the heat transmission path is high. Thus, the conventional electromagnetic relay 10 has a low heat radiation.
Additionally, in the electromagnetic relay 10, each of the terminal parts 20c, 32a and 40a and the terminals 25 and 26 has a small width and directions of extension are not the same. Accordingly, it is impossible to spot-weld the terminal parts 20c, 32a and 40a and terminals 25 and 26 to other terminals. Thus, it is difficult to use a spot-welding to mount the electromagnetic relay 10 to a relay box of an automobile.
It is a general object of the present invention to provide an electromagnetic relay in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an electromagnetic relay having a reduced height while maintaining a good voltage withstand.
In order to achieve the above-mentioned objects, there is provided according to the present invention an electromagnetic relay comprising: a base unit including a metal plate member and a base mold made of a plastic, the metal plate member having a break fixed contact point and a break terminal and being insertion-molded with the base mold; a subassembly fixed to an upper side of the base unit and including an electromagnet assembly and a movable leaf spring/armature assembly attached to the electromagnetic assembly, the electromagnet assembly including a bobbin, a coil, an iron core and a yoke, the movable leaf spring/armature assembly including a movable leaf spring having a movable contact point and an armature fixed to the movable leaf spring; and a make terminal member fixed to the base unit and having a make fixed contact point and a make terminal, wherein the base mold of the base unit has a yoke attaching part to which the yoke of the electromagnetic assembly is attached and a make terminal member attaching part to which the make terminal member is attached, and the sub assembly is mounted to the base unit by the yoke of the electromagnet assembly being attached to the yoke attaching part of the base mold, and the make terminal member is mounted to the base unit by being attached to the make terminal attaching part of the base mold.
According to the present invention, the subassembly is mounted to the base unit by attaching the yoke of the electromagnet assembly to the base mold of the base unit. Accordingly, it becomes possible to adopt a slide fit mechanism to mount the subassembly to the base unit. The slide fit mechanism for mounting the subassembly does not increase a height of the electromagnetic relay.
Additionally, since the make terminal member is fittingly attached to the make terminal member attaching part, the position of the make terminal member can be attached to the base unit with high accuracy. Therefore, it becomes unnecessary to consider the variation in the position of the make terminal member, and the height of the electromagnetic relay is reduced accordingly.
Moreover, a part of space between the yoke and the make terminal member and a part of a space between the metal plate member and the make terminal member are occupied by a part of the base mold, which gives a better insulation than a case in which the above-mentioned spaces are empty. Further, the number of factors of the variation in assembly decreases, and it becomes possible to reduce a distance between adjacent parts, which gives a low-height electromagnetic relay.
In the electromagnetic relay according to the present invention, the metal plate member may have a base plate part having the same horizontal projection size as that of the electromagnetic relay; the base mold may extend along a periphery of the base plate part and has long side base mold parts opposite to each other; each of the yoke attaching part and the make terminal member attaching part may be formed on each of the long side base mold parts; and both sides of each of the yoke and the make terminal member may be secured to the respective long side base mold parts.
According to the above-mentioned invention, the base mold is mechanically strengthened by the base plate part. Additionally, both sides of the yoke and the make terminal member are attached to the long side base mold parts. Accordingly, the yoke and the make terminal member can be attached to the base unit with high accuracy, and the mechanical strength of the attaching part is high.
Additionally, the metal plate member may have a base plate part having the same horizontal projection size as that of the electromagnetic relay; and the base mold may extend along a periphery of the base plate part and has an armature offset preventing projection, which faces a lower surface of the armature.
Accordingly, when the armature tends to greatly deform downward due to a shock applied to the electromagnetic relay, the armature offset preventing projection contacts the armature, which prevents a permanent deformation of a the movable leaf spring part to which the armature is fixed.
Additionally, in the electromagnetic relay according to the present invention, a number of each of common terminals, the brake terminals and the make terminals, which are electrically connected to the movable leaf spring, may be plural.
Preferably, the brake terminals and the make terminals, which are electrically connected to the movable leaf spring, is two; and one of the two terminals is located on one side of the electromagnetic relay and the other is located on the other side of the electromagnetic relay.
Additionally, in the electromagnetic relay according to the present invention, an end of each of the terminals may be bent outward.
Accordingly, the electromagnetic relay can be mounted to a printed circuit board by an SMT mounting method. Since a plurality of terminals are collectively provided in a small area, a thermal stress due to a difference in the thermal expansion coefficient between the electromagnetic relay and the printed circuit board can be reduced. Thus, a number of heat cycles until a soldered portion of the terminal breaks is increased, which improves the reliability of the electromagnetic relay with respect to a thermal stress.
Additionally, in the electromagnetic relay according to the present invention, each of the terminals may include a leg part and a foot part, the foot part being formed by bending each terminal to as to extend horizontally; and a width of the foot part is larger than a width of the leg part.
Since a soldering area of each terminal is increased due an increase in the width of the foot part, the terminal can be soldered to a pad of the printed circuit board with a good bonding force, and a good resistance of thermal stress can be achieved.
Further, in the electromagnetic relay according to the present invention, each of the terminals may include a leg part and a foot part, the foot part being formed by bending each terminal to as to extend horizontally; and a thickness of the leg part may be smaller than a thickness of the foot part.
Since the leg part is easily bent, a thermal stress can be relaxed, which improves the reliability with respect to a thermal stress.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.